The present invention generally relatives to the field of cryocoolers having multiple cryocooler sections and, more particularly, to allowing for the use of one charge pressure source and pressure oscillator for one cryocooler section, and for the use of at least one other charge pressure source and pressure oscillator for a different cryocooler section.
Various configurations of pulse tube cryocoolers are known for providing cooling in a number of applications. Pulse tube cryocoolers may provide cooling for electronics and the like on board extraterrestrial spacecraft. One way to categorize pulse tube cryocoolers is in relation to the number of stages that are utilized. Single stage pulse tube cryocoolers are typically operated at a comparatively high pressure for operating efficiency purposes, and can provide cooling down to about 60 K. Multiple stage pulse tube cryocoolers arranged in series (generally, where one pulse tube stage xe2x80x9cprecoolsxe2x80x9d another pulse tube stage) are usually required to realize cooling temperatures of 50 K or below. These multi-stage types of pulse tube cryocoolers are typically operated at lower pressures than the above-noted single stage pulse tube cryocoolers in order to realize a desired operating efficiency.
There are pulse tube cryocooler designs having what may be characterized as multiple cryocooler sections. For instance, a first cryocooler section may include a single pulse tube stage, while a second cryocooler section may include multiple pulse tube stages. The first cryocooler section may provide precooling for the second cryocooler section in this type of design. However, the first and second cryocooler sections utilize a common charge pressure. Therefore, it should be appreciated that using this type of pressure source may not allow the first and second cryocooler sections to each operate at a desired efficiency since both the first and second cryocooler sections will be charged at the same mean pressure. Both the first and second cryocooler sections are also exposed to the same pressure oscillation in known designs. This common pressure oscillator may be in the form of a dual-piston compressor. Compressors of this type utilize what may be characterized as opposing pistons in a common compression space. Each piston is operated at the same frequency by the same drive. However, the pistons are moved through the common compression space in opposite directions to reduce vibrations. Therefore, it should be appreciated that using this type of pressure oscillator may not allow the first and second cryocooler sections to each operate at a desired efficiency since both the first and second cryocooler sections will undergo the same pressure oscillation.
A first aspect of the present invention is generally directed to a cryocooler. This cryocooler includes at least two separate cryocooler sections (hereafter first and second cryocooler sections, although more cryocooler sections could of course be utilized). The first cryocooler section includes at least two stages, each having at least one pulse tube (hereafter first and second stages), while the second cryocooler section includes at least one stage, each having at least one pulse tube (hereafter a second cryocooler section first stage). Pressure oscillations for the first and second cryocooler sections are generated by a first pressure oscillator that is fluidly interconnected with the first cryocooler section and a second pressure oscillator that is fluidly interconnected with the second cryocooler section. The first pressure oscillator does not generate a pressure oscillation within the second cryocooler section. Similarly, the second pressure oscillator does not generate a pressure oscillation within the first cryocooler section. Stated another way, the first pressure oscillator is not fluidly interconnected with the second cryocooler section, and the second pressure oscillator is not fluidly interconnected with the first cryocooler section. Stated yet another way, the first and second cryocooler sections are fluidly isolated from each other. This then allows the charge pressures in the first and second cryocooler sections to be selected/established independently of each other. That is, the charge pressure that may be used in the first cryocooler section need not be dependent upon the charge pressure that is used in the second cryocooler section, and vice versa. Although the first and second cryocooler sections will typically each be charged with a gas, the first aspect also encompasses using any appropriate fluid. Hereafter, references will be made to having a fluid or a working fluid in the first and second cryocooler sections, each of which are closed systems.
Various refinements exist of the features noted in relation to the first aspect of the present invention. Further features may also be incorporated in the first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. Any configuration/size/type of stage may be utilized by the first and second cryocooler sections, and including having its components (e.g., one or more regenerators, one or more heat exchangers, one or more pulse tubes, one or more flow impedance devices) being of any appropriate configuration/size/type and disposed in any appropriate relative arrangement. For instance, one or more of the stages may be of the inertance-type (having an inertance tube that interfaces with one end of a pulse tube that is opposite the end of this pulse tube that interfaces with a coldhead, where the inertance tube is disposed between a fluid reservoir and this pulse tube). One or more of the stages also may be of the orifice-type (having an orifice in a fluid line that interfaces with one end of a pulse tube that is opposite the end of this pulse tube that interfaces with a coldhead, where the orifice is disposed between a fluid reservoir and this pulse tube). Any type of flow impedance device (e.g., an orifice, valve, porous plug, inertance tube, vortex tube) may be used in conjunction with each stage of the cryocooler of the first aspect. Each stage will typically have only a single pulse tube, although a stage having multiple pulse tubes would be encompassed by this first aspect.
The first cryocooler section in the case of the first aspect may be characterized as a multi-stage side of the cryocooler (e.g., the first and second stages), while the second cryocooler section may be in the form of a single stage side of the cryocooler (i.e., the second cryocooler section first stage). Such a first stage for the first cryocooler section may include a first regenerator, a first pulse tube, and first, second, and third heat exchangers. The first pressure oscillator is fluidly interconnected with the first stage, the first heat exchanger may be associated with a first part of the first regenerator (e.g., a first hot end heat exchanger), the second heat exchanger may be associated with both a second part of the first regenerator and a first part of the first pulse tube (e.g., a first cold end heat exchanger), and the third heat exchanger may be associated with a second part of the first pulse tube (e.g., a first pulse tube heat exchanger). Similarly, such a second stage for the first cryocooler section may include a second regenerator, a second pulse tube, and fourth, fifth, and sixth heat exchangers. The first pressure oscillator is also fluidly interconnected with the second stage, the first stage may precool the second stage, the fourth heat exchanger may be associated with a first part of the second regenerator (e.g., a second hot end heat exchanger), the fifth heat exchanger may be associated with both a second part of the second regenerator and a first part of the second pulse tube (e.g., a second cold end heat exchanger), and the sixth heat exchanger may be associated with a second part of the second pulse tube (e.g., a second pulse tube heat exchanger). Finally, such a second cryocooler section first stage may include a third regenerator, a third pulse tube, and seventh, eighth, and ninth heat exchangers. The second pressure oscillator is fluidly interconnected with the second cryocooler section first stage, the seventh heat exchanger may be associated with a first part of the third regenerator (e.g., a third hot end heat exchanger), the eighth heat exchanger may be associated with both a second part of the third regenerator and a first part of the third pulse tube (e.g., a third cold end heat exchanger), and the ninth heat exchanger may be associated with a second part of the third pulse tube (e.g., a third pulse tube heat exchanger). Each of these heat exchangers may be of any appropriate type/configuration.
An appropriate heat transfer link may be provided in any appropriate manner between the first heat exchanger of the above-described first stage of the first cryocooler section and the seventh heat exchanger of the above-described second cryocooler section first stage in the case of the first aspect. Although this will typically be through conductive heat transfer (e.g., where the first heat exchanger and seventh heat exchanger are mounted on a common flange, plate, or the like; where the first heat exchanger and seventh heat exchanger are connected by a copper rope), convective heat transfer techniques or a combination of convective and conductive heat transfer techniques could be utilized as well. An appropriate heat transfer link may also be provided in any appropriate manner between the second heat exchanger of the above-described first stage of the first cryocooler section and the eighth heat exchanger of the above-described second cryocooler section first stage. Although this will typically be through conductive heat transfer (e.g., where the second heat exchanger and eighth heat exchanger are mounted on a common flange, plate, or the like; where the second heat exchanger and eighth heat exchanger are connected by a copper rope), convective heat transfer techniques or a combination of convective and conductive heat transfer techniques could be utilized as well. Both of these heat exchanger pairs may also be thermally connected by conductive heat transfer in any appropriate manner as well (i.e., a combination of the foregoing).
The first pressure oscillator and the second pressure oscillator may generate a common pressure oscillation or different pressure oscillations in their corresponding first and second cryocooler sections in the case of the first aspect. First and second charge pressures may be used in the first and second cryocooler sections, and these may be of the same magnitude or of different magnitudes. The same or a different fluid pressure amplitude may be generated in the first and second cryocooler sections via operation of the first and second pressure oscillators, respectively. The same fluid types or different fluid types (e.g., the same or different working fluid) may be used in the first and second cryocooler sections as well. Any combination of the various options presented in this paragraph may be utilized as well.
The first and second pressure oscillators utilized by the cryocooler of the first aspect may be in the form of separate compressors (e.g., first and second compressors). One option would be to run the first and second compressors at the same or a common frequency. Another option would be run the first and second compressors at different frequencies. The above-noted options with regard to charge pressures, fluid pressure amplitudes, and fluid types may of course be used with one or both of these two options as well.
The first and second pressure oscillators utilized by the cryocooler of the first aspect may also be in the form of a single compressor that is xe2x80x9csplit,xe2x80x9d for instance into a high-pressure side and a low-pressure side. Such a compressor may include first and second pistons, as well as first and second compression spaces that are fluidly isolated from each other. The first and second pistons may be interconnected with a common control system (e.g., a common controller or control electronics) that at least operatively interfaces with each of the first and second pistons. For instance, this common control system or controller may interface with a first motor for moving the first piston, as well as with a second motor for moving the second piston. In any case, the first piston is advanced through the first compression space to generate a pressure oscillation in the first cryocooler section. Similarly, the second piston is advanced through the second compression space to generate a pressure oscillation in the second cryocooler section. A single piston (the first piston) may be advanced through the first compression space, while a single piston (the second piston) may be advanced through the second compression space to provide pressure oscillations in the first and second cryocooler sections. In one embodiment, the first and second pistons are disposed in opposing relation (for movement along a common axis) and are moved in opposite directions to reduce vibration of the compressor. Moreover, in one embodiment, a low-pressure side of this split compressor interacts with the first cryocooler section, while a high-pressure side of the split compressor interacts with the second cryocooler section.
The first and second cryocooler sections may be xe2x80x9cthermally connectedxe2x80x9d in any appropriate manner in the case of the first aspect. Consider the case where the first cryocooler section includes first and second stages each having a pulse tube, and where the first stage of the first cryocooler section precools the second stage of the first cryocooler section. The second cryocooler section first stage may not only provide cooling to a particular cooling load, but may also provide precooling for the second stage of the first cryocooler section. Stated another way, the second cryocooler section first stage may assist the first stage of the first cryocooler section to pre-cool the second stage of the first cryocooler section.
There are a number of advantages associated with the arrangement contemplated by the first aspect. Any number of parameters may be independently selected in relation to both the first and second cryocooler sections to achieve a desired result. For instance, the first cryocooler section may be operated so as to provide cooling over a first temperature range (including both at a single temperature, but more likely over a range of temperatures) and the second cryocooler section may be operated so as to provide cooling over a second temperature range (including both a single temperature, but more likely over a range of temperatures) that is different from the first temperature range. In one embodiment, the first cryocooler section provides cooling to a lower temperature than the second cryocooler section (e.g., the first cryocooler section may provide cooling at a lower temperature to a cooling load than the second cryocooler section provides cooling to a different cooling load). The second cryocooler section also may be operated at a higher charge pressure than the first cryocooler section, for instance such that both the first and second cryocooler sections may operate at a more desired efficiency. More generally, the first cryocooler section and the second cryocooler section may be operated at one or more of a different charge pressure, a different pressure amplitude, a different pressure oscillation frequency, using a different working fluid, or any combination thereof (i.e., each of these four parameters may be independently selected for both the first and second cryocooler sections). The flexibility provided by using separate fluid volumes (e.g., first and second cryocooler sections that are fluidly isolated from each other) may be applicable to any pulse tube stage configuration of any kind.
A second aspect of the present invention is generally directed to a cryocooler having at least two separate cryocooler sections (hereafter first and second cryocooler sections, although more cryocooler sections could of course be utilized). Another component of the cryocooler is a single compressor. This compressor includes first and second pistons, as well as first and second compression spaces that are fluidly isolated from each other. The first piston is advanced through the first compression space to interact with fluid in the first cryocooler section (typically a gas, although the second aspect encompasses having any appropriate fluid in the first cryocooler section). Similarly, the second piston is advanced through the second compression space to interact with fluid in the second cryocooler section (typically a gas, although the second aspect encompasses any appropriate fluid in the second cryocooler section).
Various refinements exist of the features noted in relation to the second aspect of the present invention. Further features may also be incorporated in the second aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. Both the first and second cryocooler sections may be in the form of a closed system. There are a number of characterizations relating to the single xe2x80x9csplitxe2x80x9d configuration for the compressor contemplated by the second aspect. The first and second pistons may be interconnected with a common control system (e.g., a common controller or control electronics). In one embodiment, this common control system at least operatively interfaces with each of the first and second pistons. For instance, this common control system may interface with a first motor for moving the first piston, as well as with a second motor for moving the second piston. Another characterization of the single xe2x80x9csplitxe2x80x9d configuration for the compressor is that a single piston (the first piston) advances through the first compression space and provides the pressure oscillation within the first cryocooler section, while a single piston (the second piston) advances through the second compression space and provides the pressure oscillation within the second cryocooler section. The first and second pistons in this case are preferably disposed in opposing relation (for movement along a common axis) and move/advance in opposite directions to reduce vibrations.
The first and second cryocooler sections used by the second aspect each may be of any appropriate configuration/size/type (e.g., a Stirling-type cryocooler, a pulse tube-type cryocooler; a hybrid combination of pulse tube and Stirling stages). One or both of the first and second cryocooler sections each may also be at least one stage, each of which has at least one pulse tube. Any configuration/size/type of stage may be utilized by the first and second cryocooler sections in the case of the second aspect, including having its individual components being of any appropriate configuration/size/type and disposed in any appropriate relative arrangement. For instance, any pulse tube stage used by the second aspect may be of the inertance-type (having an inertance tube that interfaces with one end of a pulse tube that is opposite the end of this pulse tube that interfaces with a coldhead, where the inertance tube is disposed between a fluid reservoir and this pulse tube). Any pulse tube stage used by the second aspect also may be of the orifice-type (having an orifice in a fluid line that interfaces with one end of a pulse tube that is opposite the end of the pulse tube that interfaces with a coldhead, where the orifice is disposed between a fluid reservoir and this pulse tube). Generally, any type of flow impedance device may be utilized by any pulse tube stage that is utilized by the second aspect (e.g., an orifice, valve, porous plug, inertance tube, vortex tube).
Consider the case where the first and second cryocooler sections of the cryocooler of the second aspect each include at least one stage, each having at least one pulse tube. The first cryocooler section in the case of the second aspect may be characterized as a multi-stage side of the cryocooler (e.g., first and second stages), while the second cryocooler section may be in the form of a single stage side of the cryocooler (i.e., a second cryocooler section first stage). Such a first stage for the first cryocooler section may include a first regenerator, a first pulse tube, and first, second, and third heat exchangers. The first compression space and first piston interact with the fluid within the first stage, the first heat exchanger may be associated with a first part of the first regenerator (e.g., a first hot end heat exchanger), the second heat exchanger may be associated with both a second part of the first regenerator and a first part of the first pulse tube (e.g., a first cold end heat exchanger), and the third heat exchanger may be associated with a second part of the first pulse tube (e.g., a first pulse tube heat exchanger). Similarly, such a second stage for the first cryocooler section may include a second regenerator, a second pulse tube, and fourth, fifth, and sixth heat exchangers. The first compression space and first piston also interact with the fluid within the second stage, the first stage of the first cryocooler section may precool the second stage of the first cryocooler section, the fourth heat exchanger may be associated with a first part of the second regenerator (e.g., a second hot end heat exchanger), the fifth heat exchanger may be associated with both a second part of the second regenerator and a first part of the second pulse tube (e.g., a second cold end heat exchanger), and the sixth heat exchanger may be associated with a second part of the second pulse tube (e.g., a second pulse tube heat exchanger). Finally, such a second cryocooler section first stage may include a third regenerator, a third pulse tube, and seventh, eighth, and ninth heat exchangers. The second compression space and second piston interact with the fluid in the second cryocooler section first stage, the seventh heat exchanger may be associated with a first part of the third regenerator (e.g., a third hot end heat exchanger), the eighth heat exchanger may be associated with both a second part of the third regenerator and a first part of the third pulse tube (e.g., a third cold end heat exchanger), and the ninth heat exchanger may be associated with a second part of the third pulse tube (e.g., a third pulse tube heat exchanger). Each of these heat exchangers may be of any appropriate type/configuration. In one embodiment, a low-pressure side of the split compressor of the second aspect interacts with the first cryocooler section, while a high-pressure side of this split compressor of the second aspect interacts with the second cryocooler section.
An appropriate heat transfer link may be provided in any appropriate manner between the first heat exchanger of the above-described first stage of the first cryocooler section and the seventh heat exchanger of the above-described second cryocooler section first stage in the case of the second aspect. Although this will typically be through conductive heat transfer (e.g., where the first heat exchanger and seventh heat exchanger are mounted on a common flange, plate, or the like; where the first heat exchanger and seventh heat exchanger are connected by a copper rope), convective heat transfer techniques or a combination of convective and conductive heat transfer techniques could be utilized as well. Conductive heat transfer may also be provided in any appropriate manner between the second heat exchanger of the above-described first stage of the first cryocooler section and the eighth heat exchanger of the above-described second cryocooler section first stage. Although this will typically be through conductive heat transfer (e.g., where the second heat exchanger and eighth heat exchanger are mounted on a common flange, plate, or the like; where the second heat exchanger and eighth heat exchanger are connected by a copper rope), convective heat transfer techniques or a combination of convective and conductive heat transfer techniques could be utilized as well. Both of these heat exchanger pairs may also be thermally connected by an appropriate heat transfer link in any appropriate manner as well (i.e., a combination of the foregoing).
The first piston and first compression space of the compressor may be characterized as a first pressure oscillator, while the second piston and second compression space of the compressor may be characterized as a second pressure oscillator. The first pressure oscillator and the second pressure oscillator may generate a common fluid pressure oscillation or a different fluid pressure oscillation in their corresponding first and second cryocooler sections in the case of the second aspect. First and second charge pressures may be used in the first and second cryocooler sections, and these may be of the same magnitude of a different magnitude. The first and second pistons may also generate a common fluid pressure amplitude or a different fluid pressure amplitude in their corresponding first and second cryocooler section. The same fluid types or different fluid types (e.g., the same or different working fluid) may be used in the first and second cryocooler sections as well. Any combination of the various options presented in this paragraph may be utilized.
In one embodiment of the second aspect, the compressor moves the first and second pistons at a common frequency. The compressor also may be configured to move the first and second pistons in opposite directions (e.g. to reduce vibration of the compressor). Finally, the compressor of course may move the first and second pistons both at a common frequency and in opposite directions. In each of these instances and in order to enhance the reduction of vibration, the first and second pistons may be disposed in opposing relation (i.e., so as to move along a common axis).
The first and second cryocooler sections may be xe2x80x9cthermally connectedxe2x80x9d in any appropriate manner in the case of the second aspect. Consider the case where the first cryocooler section includes first and second stages, where the first stage of the first cryocooler section precools the second stage, and where the second cryocooler section has a single pulse tube arrangement. The second cryocooler section may not only provide cooling to a particular cooling load, but may also provide precooling for the first cryocooler section.
There are a number of advantages associated with the arrangement contemplated by the second aspect. Any number of parameters may be independently selected in relation to both the first and second cryocooler sections to achieve a desired result. For instance, the first cryocooler section may be operated so as to provide cooling over a first temperature range (including both a single temperature, but more likely over a range of temperatures) and the second cryocooler section may be operated so as to provide cooling over a second temperature range (including both a single temperature, but more likely a range of temperatures) that is different from the first temperature range. In one embodiment, the first cryocooler section provides cooling to a lower temperature than the second cryocooler section (e.g., the first cryocooler section may provide cooling at a lower temperature to a cooling load than the second cryocooler section provides cooling to a different cooling load). The second cryocooler section also may be operated at a higher fluid charge pressure than the first cryocooler section, for instance such that both the first and second cryocooler sections may operate at a more desired efficiency. The flexibility provided by using this type of xe2x80x9csplit compressorxe2x80x9d may be applicable to multi-section cryocoolers of any appropriate kind.